Material container for dental furnaces



Sept. 22, 1931. O, A COLBY 1,823,968

MATERIAL CONTAINER FOR DENTAL FURNACES Original Filed Feb. 14, 1928 2 Sheets-Sheet 1 I/ III Il INVENTOR TORNEY Sept. 22, 1931. o. A. COLBY v MATERIAL CONTAINER FOR DENTAL FURNACES 2 Sheets-Sheet 2 Original Filed Feb. 14, 1928 Ray 4 lNVENTOR 01': A. Colby ATTORNEY Patented Sept. 22, 1931 UNITED STATES:

PATENTLOFFICEA 1 ORA A. COLBY, OF MANSFIELD, OHIO, .ASSIGNOR TO WESTINGHOUSE ELECTRIC 8'6 MANUFACTURING COMPANY, A CORPORATION OF "PENNSYLVANIA 1 cessful.

MATERIAL CONTAINER FOR DENTAL FURNACES 1 Original application filed February i4, 1928, Serial No. 2 54,208. Divided and this application filed May 1,

' 1930. Serial This application is a divisionof my application, Serial No. 254,208, filed February 14, 1928. y

My invention relates to electric furnaces and more particularly to material containers for electrically-heated furnaces adapted. for use in dental laboratories for the heat treatment or glazing of artificial teeth; I

In the practice of dentistry, it is common for the dentist either to construct special porcelain teeth or to purchase manufactured porcelain teeth and cut or grind them to a de-' sired size and shape. the cutting and grinding operations, however, the glazed'surface of the tooth is destroyed and voids are exposed, in which bacteria :and food deposits vmay collect and result inadiscoloration of the tooth. It becomes necessary, therefore, to apply a coating to'the tooth which may glazed to cover the voids. Further, it is necessary, in some instances, tostain or color portionsof an artificial tooth to make'it harmonize in color with the natural teeth.

All of these procedures involve heat-treatment, and have usually been efl'e'cted by employing an electric-resistance furnace hav ing a heating element composed of platinum wire. In view of the inherent expense of such a furnace, it has been attempted to employ resistance heating elements composed ofvarious iron alloys, and particularly those containing nickel and chromium, but the applications haveinvariably proved to be unsuc- Various methods of construction have been employed in attempting to utilize a nickelchromium alloy for this pu'rpos'e. In one con-* struction, the resistance element was com pletely separated from the work to be heated by a mufile substantially covering the side walls of the heating chamber; This method proved objectionable in view of the time res quired to bring the furnace up to operating temperature, which undesirably lengthened the time of the cycles of operation. In another construction the heating element was embedded in the sidewalls of the furn'ace chamber, but, at the relatively high operating temperature desired (approximately 1950 the element rapidly burned out and the construction roved to be impracticable from a cost stan point. j

In another construction, theheating elementwas so disposed upon the walls of the heating chamber that the work to-be heated was directly exposed to heat radiating therefrom, This construction was found to be objectionable because theelement spalled, responsive to repeated heating and cooling, and flakes of material cast therefrom stained and spotted the light-colored porcelain, re-

sulting in a worthless product.

An object of the present invention, there fore, isthe provision of a dental furnace so constructed that the use of a commercial t pe fvide, in a dental furnace, means for protecting the work tobe heated which is removable from the heating chamber, and which has a suiiiciently low heat-storage capacity whereby the work maybe enclosed and protected during the heating and cooling operations withouta substantialincrease in'time in the cycles of operation. 'In' practicing my invention, I provide a relatively small heating chamber, meansfor supporting a nickel-chromium resistance 'le't ment on the longitudinal walls and floor thereof, means for minimizing the spalling of material from the walls and resistance element, and an improved means for protecting the tooth during the heating and cooling operations. i In the accompanying drawings, 'Fig'ure l is a view, in front elevation, of a dental furnace embodying my invention, Fig. 2 is aview, invertical longitudinal section, taken'on the line IIII of Fig. 1, Fig. 3 is a'view, in end elevation, of a resistor support constituting a part of my invention,

a Fig. 4 is a view, in longitudinal section, taken on the line'IV- IV'of Fig. 3 v

Fig. 5 is a plan view of a work-supporting tray," i a f 65 of resistance heating'element is practice le, and wherein the work being heated is at all Referring; more particularly to the draw ings, a furnace embodying my invention com prises a pair of cast metallic plates;1; and 2' and a metallic shell 3, disposed therebetween,

constituting a metallic furnace casing;-- .The

lower portion of the cas ing is c losed ly a plate 4', of "electri c insulati ng material,;con-"' stituting a terminal block, as hereinafter described. The casing is maintained in assembled relation by means of it, plurality of clamping bolts 5 extending longitudinally therethrough. The castcmetallic plate ;.1' is provided with an opening to afford access to the interior of-the casing. I

Within the. casing are disposed a plurality of blocks 7 and 8 of'inolded ceramic :heat-,

insulating material defining a furnace chann ber '9.

Theblock 8 comprises arched portion 10', constituting the roofand side, wall p on.

.tions of the chamber, and a flat horizontally extendingportion ll'integral therewith, constituting the fioor of the chamber. I, A plate 12, composed of a close-grained highly refractory material, such as porcelain, ispartially embedded in thewinner face of the block 7 and. is substantially coextensive in area withthe lateral dimensions ofmthe furnace chamber. The block is molded in a single piece, and the plate 12, which has been preformed, is embeddedtherein in the molding' loperation. The block plate are thenbaked. as av unit and the resulting structure is a substantially unitary block havinga portion of one face thereof composed of highly refractory material. v f The block 8 is {enlarged adjacent to the forward portionthereofand extends a short distance toward the longitudinalQaxisiof the furnace, as shown more particularly in Fig. 2, and a facin 13 of porcelain is disposed peripherally of the edge of the opening de fined thereby. The porcelainis appliedto the block.8 duringthe molding operation thereof, and the result, as infthe. case of the block 7, is a substantially integral structure.

The opening. defined by the forward edge of the blocks 8 cooperates with the opening in'the cast plate 1 toqpermit charging and removing material with respect to the furnace chamber. 7 V f The charging opening is normally'closed, during'the heating operation, .by abloick 14 of heat-insulating material which is provided witha facing, or cap-15,- ofporcelain, molded upon the inner facethereof inamanner similar-to theporcelain facings 12 and 13.; When V in operative position, the closure 14 fits relasupported upon a flange 17 cast integral with the plate 1. Manipulation of the closure is facilitated by means of an enlarged rib, extending vertically thereof, constituting a handle. A peephole 18 extends through the closure-block 14. to permit the observation of conditions in the furnace chamber, and may benormally closed, if desired, by a removable. refractory plug (not shown) in a =.well-'lgno,\vnjmanner.

The heating element20 comprises an electrical-resistancewire of refractory metallic material, such as anickehchromium alloy, wound/meme ferns-of an elongated helix; -Th'e' specific form of the element is obviously immaterialandmay be varied as desired to Ineetjthe requirements of a; particular installation. p

The heatingelement 2 0 is supported in operative position by means of a. shell 21, shown in detail in Figs. 3jand 4 composed of a closegrain'edj highly refractory material, such as porcelain, and provided with a plurality of horizontally extending grooves on the inner surface.,tl1ereof. .The heating element is threaded through the rooves and operatively supported therein I i The groovesare somewhat restricted in lateral area adjacent to the innerrsurface' of theshell a nd thereby serve the double purpose, of maintaining the heating element ther ein 'andof reducing to a minimum the amount of material cast from the element into the heatingchamber, responsive to the spallthereof, consistent with the obtaining of a desired amount of direct heat radiation fro nthe; element.

"The-outer dimensions of the shell 21 are such thatthe'rooflfioor and side walls of the heatiii g'ichamber, partially defined by blocks 17 and 8,,are completely covered and the ends oflthe. shell cooperate with the plate 11 and porcelainfacings 12 and'13, to constitute a heatingcha nber, the walls of which are composed of a. close-grained thermally-insulating material having highly refractory characteristics. y l

heating element may comprise a plurality'o'f section's'of resistor wire adap ed to be independently connected in an electric circuit'to effect a desired temperature control, butiII prefer, in the present embodiment, to employ a single continuous element. The ends, oflthe ,element are connected, respectively, totwojte'rminal posts 22 secured to the terminal blocke toggle snapswitch, 23, of a usual type, issecured to the cast plate 1 in such manner that'the operating lever 24 thereofprojects through saidplate; A terminal lead 25 is electrically; connected, at the respective ends thereof,'to-oneof the terminal posts 22 and to termi ator switch 23. :Leads 26, and 27 ,from'a suitable source of power, are connected, respectively, to the other terminal of switch 23 and to the other terminal post 22 and extend through a suitable opening in the cast plate 2. The opening is bushed to protect the leads against abrasion, in the usual manner.

With the construction described, the resistor-supporting shell and the resistor eledrawn longitudinally.

The work to be heated (an artificial tooth in the present embodiment) is supported within the heating chamber upon a removable tray 28 which is constructedof porcelain, or other suitable highly refractory material.

The tray is provided with a vertical flange or bead 29, upon the'upper surface thereof,

adapted to surround the work, and laterally extending beads 30 on the under surface thereof, constituting spaced supports for the tray. One end of'the tray is elongated, as at 28a, and in a plane substantially higher than the body of the tray, to provide means for facilitating the handling thereof incident to moving the same into and out of the heating chamber. 1

A cover, or cap, 31, comprising relatively thin walls of highly refractory material, is substantially coextensive in horizontal sec tion with the outer dimension of the bead 29, and is adapted to cooperate therewith to completely enclose the work.

A vertically-projecting flange or lug 32 is formed integral with the cover at one end thereof to facilitate handling, and a horizontally extending flange or rim 33 is formed on the lower peripheraledge of the cover.

A depression 34 is provided in the upper surface of the lug 32 and is adapted to contain a temperature-indicating means, such as a gold pellet, as hereinafter described.

It is to be understood that the tray 28 and cover 31 are of very thin material and, although oifering substantially no hindrance to the flow of heat therethrough, are sufficiently refractory to withstand the relatively high operating temperature of the furnace chamber.

In operation, the artificial tooth to be heat-treated or glazed is suitably supported upon the tray 28 and the cover 31 is placed in operative position. A fusible material, preferably a piece of gold'foil, is placed in the depression. 34 in the cup, and the tray and cup are placed in the heating chamber, which has been heated to a desired degree.

It is desirable, in the present instance, to subject the work to a temperature of approx imately 1950 F., and, since this temperature is approximately the melting point of gold, the melting of the gold foil in the depression 34: affords a reliable indication of the attain mentof the proper'operatin'g temperature. The condition of thezgold foil may be observed. through the peephole 18 in the closure block-l4. I

perature, the closure block'is removed, and the work-supporting tray and cover are removed from the chamber andpermitted to cool freely in the air. Thecover maybe Upon the attainment of the desired tems maintained in operative position during a :,fi

portion of the cooling period to prevent cracking of the surface of the heated tooth resulting from the contact of cold air therewith. i

During the heating operation, particles are cast, from the heating element and chamber walls, and, in view of the finely divided character thereof, contamination of the work thereby is prevented with difficulty. By

constructing the furnace chamber walls of a 1;;

close-grained porcelain, and employing a substantially non-oxidizable heating element, the amount of material spalling therefrom may be eflectively reduced. Irrespective of the quality of the materials, however, $531 a certain amount of spalling occurs and the particles cast off are circulated through the chamber by convection currents therein.

By my mvention, however, the work is maintained out of contact with the furnacechamber atmosphere at all times and the work is adequately protected from the relatively small amount of spalled material circulating in the furnace chamber atmosphere.

Although the heat-storage effect of the tray and cover is sufficiently small to offer substantially no resistance to the flow of heat therethrough, it is suflicient to. effect quick heating and consequent expansion of I the air within the cover and thereby main- =1 too rapid cooling of the surface of the tooth is prevented.

The novel details of construction of the furnace proper is claimed in my original application for Letters Patent, Serial No. 254,208, filed February 14, 1928.

Various modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are set forth by the prior art and 1 imposed by the appended claim. 7

I claim as my invention In a dental furnace, means for supporting and protecting an artificial tooth during the heating and cooling the reofincluding asu'p; portingtray and a cover therefor of highly refractory'material, means cooperating with the cover to constitute .a substantially dustproof enclosure for said tooth, integral handling means on the cover, and a depression at the junction of the handling means and the cover to receive a temperature-indi eating rneans.

In testimony whereof, I have hereunto subscribed niy name this 21 day of April ORA A. COLBY. 

